1. Field of the Invention
The present invention relates to a scroll compressor suitable for a refrigeration circuit included in a vehicle air conditioning system.
2. Description of the Related Art
The scroll compressor includes a fixed scroll and a movable scroll that makes a revolving movement with respect to the fixed scroll. The movable and fixed scrolls form a compression chamber in cooperation with each other. The revolving movement of the movable scroll continuously causes the process of sucking a refrigerant serving as working fluid into the compression chamber, the process of compressing the sucked refrigerant in the compression chamber, and the process of discharging the compressed refrigerant from the compression chamber. For this discharge process, the fixed scroll is provided with a discharge hole near the center thereof.
Specifically, the fixed and movable scrolls have their respective end plates and spiral walls protruding from the end plates. The discharge hole is formed in the end plate of the fixed scroll. The compression chamber is formed in between the fixed spiral wall of the fixed scroll and the movable spiral wall of the movable scroll.
The scroll compressor disclosed in Unexamined Japanese Patent Publication No. 10-9157 further includes tip seals mounted to the end faces of the fixed and movable spiral walls, and bottom sheets are laid on the inner faces of the end plates of the fixed and movable scrolls. The tip seal of the movable spiral wall slides against the bottom sheet of the fixed scroll, whereas the tip seal of the fixed spiral wall relatively slides against the bottom sheet of the movable scroll. These tip seals and bottom sheets increase the airtightness of the compression chamber, namely refrigerant compression efficiency.
Pressure in the compression chamber rises as the compression chamber moves toward the discharge hole, and is maximized at the terminal stage of the compression process. Therefore, the inner end portions of the fixed and movable spiral walls as viewed in the radial directions of the fixed and movable scrolls receive a high reactive force due to a compressed refrigerant at the terminal stage of the compression process. The inner end portions are therefore required to have enough strength to endure the compression reactive force.
For that reason, like the scroll compressor disclosed in Unexamined Japanese Patent Publication No. 10-68392, the arc-shaped inner end portions of the fixed and movable spiral walls are thicker than the other portions of the spiral walls, and have a stepped shape. More specifically, each of the inner end portions has a base portion located on the end plate side of the corresponding scroll and a top portion located on the bottom sheet side of the counterpart of the above scroll. The base portions have greater width than the top portions do.
In the case of the scroll compressor disclosed in the Publication, the inner end portions of the fixed and movable spiral walls have the same shape and size. Therefore, based on the boundary between the inner end portion of the fixed spiral wall and the other portions, that is, a seal-off point between an involute curving face forming the inner face of the other portions in the fixed spiral wall and the arc-shaped face forming the inner face of the inner end portion of the fixed spiral wall, the location of the discharge hole, the size of the bottom sheet of the fixed scroll and the location of an inner end portion of the movable tip seal mounted onto the movable spiral wall are primarily determined in this order.
The location of the inner end portion in the movable tip seal is an important factor that determines the refrigerant compression efficiency. Therefore, the compression efficiency of the scroll compressor disclosed in the Publication is automatically determined only by the seal-off point, which makes difficult further improvement of the compression efficiency.